Elevator call and automatic leveling system



P 23, 1954 H. E. HANCOCK ET AL ELEVATOR CALL AND AUTOMATIC LEVELING SYSTEM 3 Sheets-Sheet 1 Filed March 29 1951 1 lllllllllllllllllllllllllllll ll INVENTORS.

Mimi Q. .JMA

ATTOZNEYS.

P 1954 H. E. HANCOCK ET AL 2,690,236

ELEVATOR CALL AND AUTOMATIC LEVELING SYSTEM Filed March 29, 1951 3 Sheets-Sheet 2 INVENTORS.

M M 4. JM

ATTORNE Y5.

Sept. 28, 1954 H. E. HANCOCK ET AL 2,690,236

ELEVATOR CALL AND AUTOMATIC LEVELING SYSTEM Filed March 29, 1951 3 Sheets-Sheet 5 INVENTORS.

$0 mmu v mm 93 3 P OFU m3 m. H3 5 N3 30 m6 Patented Sept. 28, 1954 ELEVATOR CALL AND AUTOMATIC LEVELING SYSTEM Harold E. Hancock, Lovelaiid, and Carl A. Schneider, Cincinnati, Ohio, assignors to The Shepard Elevator Company, Cincinnati, Ohio, a corporation of Ohio Application March 29, 1951, Serial No. 218,134

20 Claims. 1

This invention relates to elevators and is particularly directed to a novel call and automatic leveling system by means of which an elevator cab may be brought into accurate vertical alignment with the various floors of a building.

disadvantage that it requires a relatively expensive motor-generator set in addition to the elevator motor.

On the other hand, those methods of elevator control which have hitherto been used with ele- It is highly essential that an elevator cab can vators driven by alternating current, single speed be brought into close alignment with each of motors, or motors having a small number of the floor levels at which it is stopped. If the fixed speeds have either been only partially eiiecmisalignment between the cab and floor is altive in their function, allowing too much mislowed to exceed more than a small fraction of alignment, or have required considerable coran inch, an inherently dangerous situation is rective jogging to compensate for the undercreated in that careless or infirm passengers are travel or overtravel of the elevator cab with reliable to stumble and fall when entering or leavspect to the floor. Furthermore, the leveling deing the cab. Furthermore, if the elevator is vices heretofore employed have been complex, being used to carry heavy freight, the cab and expensive to install and dimcult to maintain. floor must be accurately leveled or it will be imn a typ at Controller em Of e possible to roll or slide goods from the car onto yp p us p oyed, the circuits to the the floor. elevator motor switches are controlled mechani- An additional consideration is that modern all'y through abrush-commutator arrangem high speed elevators are impractical unless the the commutator providing a Series of switch C011- stopping and leveling operations can be accomtacts corresponding to the levels at which the plished proportionally as rapidly as the actual car is to stop. The CO t y b driven floor-'to-fioor speed of the cab itself, '11-, is 'fur in synchronism with the car relative to stationther desirable that leveling can be accomplished y brushes, 1' Contacts, corresponding to variin a single smooth continuous motion; that is, 0 8 pp positions 0n the other hand, the cab should slide into the floor level and then a ies o brushes may be translated in synstop at a point in alignment with the selected chronism with the car relative to a stationary floor. Single motion cab positioning is preferable commutator having one or more stop Se me tssince it is quicker and also much smoother than In either Case, a circuit 170 the evator motor that type of positioning in which the cab stops d brake Solenoid, mOre p c fic y to the out of level with the fl r nd whi h e ui elevator motor and brake solenoid controlling several corrective jogs to bring it into alignment. SWitcheS, maintained so long s the brush and smoothness of operation may even be er energized portion of the commutator are in conmount consideration in certain installations tact and the circuit is disrupted as the brush or where deli t apparatus i being moved or as brushes serially leave the energized section and in hospitals where it could be quite harmful for engage e insulated p t- It is necespatients t b jarred, sary that the stop segment be sufficiently long Several methods of automatic elevator leveling to permit the brush to ride 11. t at least a are entl i some of th 11 known types distance corresponding to the average distance being adopted solely for use with direct current, t'l'avelled y the Car in Com ng to a stop after variable speed elevator motors. An elevator cab 40 power disruption W Ve a Stop segment long which is raised or lowered by a variable speed enough to accommodate the average glide, may, motor is much easier to lev l properly than one because of the variations in the distance travhaving a single speed drive, since an adjustable elled by the car after D disruption, p t speed motor permits rapid cab movement for a the be undesirably nd even badly mislarge portion of the cab travel while allowing aligned with the floor. the speed of the cab to be greatly reduced upon As one example of a more c mpli a d arapproaching the selected floor so that the cab ng ment, a second series of elements is promay be driven slowly into the proper floor level. vided on the commutator to act as secondary Usually, however, a variable speed motor recircuit makers through which the elevator motor quires a rheostat, or as in the Ward Leonard sysmay be subsequently reenergized if the brush and tem, a high speed auxiliary motor-generator set. stop segments (and hence the car and building The electrical power loss caused by the high floor) are not aligned properly when the car resistance of the rheostat makes it uneconomical, comes to rest. A control system of this type re- While the Ward Leonard system has the obvious quires that many difierent brush-commutator tional to the velocity of the cab) depending upon the brake).

reference), and the tachometer signal (propor- It is obvious that for any given distance between the floor and cab, that an increase in cab velocity will be accompanied by a corresponding decrease in the error voltage, or viewed differently, the higher the cab velocity the greater the distance from the floor level at which the error voltage will become zero. Zero error voltage is reached and the brake is thus applied at a distance from the floor determined by the car velocity.

Another important objective of the present invention has been to provide a control circuit which compensates for the variance in the frictional coefiicient of the brake. Since a frictional brake is considerably more effective at slow speeds than at high ones, the required sliding or braking distance increases all out of proportion to an increase in cab velocity. The compensation for this is effected by including a resistance network in the control circuit which causes the tachometer signal to vary as the nth power of the cab velocity (n=some number greater than 1 As a result the error voltage will become zero and the brake will be applied at a distance from the floor which is proportional to the nth power of the cab velocity. By properly selecting n, the braking point may be controlled so that regardless of the load, the elevator will level with the fioor in one continuous motion without any corrective jogs.

An additional objective of this invention has been to provide a control circuit which will prevent the motor from being plugged i. e. being connected in reverse while mechanically running forward, if for some reason the cab should overshoot the floor. Once the error voltage has reached zero and the motor circuit is opened, it is prevented from closing again until the cab has come to rest.

While this invention has been discussed primarily with respect to elevators driven by single speed alternating current motors, it will be appreciated that its use may be advantageous in many diverse installations involving similar problems of control and leveling. The principles of the present invention are fully applicable to single speed, two speed, multi-voltage and variable voltage alternating or direct current systems, and those skilled in the art will readily comprehend the various modifications to which this invention is susceptible.

Other objects and advantages of my invention will be apparent from a further consideration of the specification in conjunction with the drawings in which:

Figure 1 is a greatly simplified schematic diagram of the call and leveling circuit, and

Figure 2 is a schematic circuit diagram of the call and automatic leveling system.

Figure 3 is a diagrammatic view for use in conjunction with Figure 2, showing the relays and their associated contacts, the contacts being shown in the same vertical relationship on the page as the contacts in Figure 2.

The leveling system, as shown in simplified schematic form in Figure 1, includes main power supply lines 10, l l and [2 which energize a motor and a brake solenoid shown generally at I3. Control of the power circuits to the motor and brake solenoid I3 is maintained by up and down contactors l4, 15. These contactors either open the motor and brake solenoid circuit or close the power circuit so that the brake will be released and the motor will operate to drive the cab toward the selected floor.

A control voltage is supplied through lines l6 and I1 across a variable resistance [8 and a potentiometer l9 connected in parallel. The variable resistance [8 is provided with a plurality of taps 2B, the particular tap which is connected to line 2| being determined by the depression of a call button associated with the floor selected. The magnitude of the voltage drop across the resistance I8 is made proportional to the height of the selected floor above the bottom of the shaft. The potentiometer I9 has a tap 22 which is moved relative to the potentiometer coil in synchronism with the cab movement so that the voltage drop of the potentiometer is proportional to the distance of the cab above the bottom of the shaft.

An error voltage representing the difference in height between the cab and the selected floor is thus obtained across line 2| and tap 22. This error voltage will be zero when the voltage drops across the potentiometer and variable resistance are equal, that is, when the cab is properly aligned With the selected floor. If the cab is not levelled at the selected floor, the error voltage will be proportional in magnitude to the distance between the cab and the selected floor and will have a plus or minus polarity indicating whether the cab is above or below the floor.

A tachometer, or small direct current generator 23, is inserted in line 2| in series with the floor level signal. The tachometer 23 is mechanically interconnected with the motor 13 and has the characteristic that it generates a voltage signal which is proportional to the speed of the cab. The polarity of the tachometer 23 is such that when the car is running toward the selected floor,

the tachometer voltage is opposed to the floor position voltage and hence subtracts from it in the same way as the cab position signal. Consequently, the greater the cab velocity the lower the difference which will obtain between the floor level signal and the car position signal. The tachometer signal thus causes the error voltage to reach zero before the cab actually levels with the floor and the distance from the floor at which the error voltage reaches zero is made proportional to the velocity of the cab.

The error voltage is connected .to the input side of an amplifier 24 through leads 2 I, 25. The output characteristic of the amplifier 24 is such that for one polarity of error voltage the up relay contact 14 will be energized, for the opposite polarity the down relay contact It will be energized. Whenever either of these contacts is energized, the line voltage is supplied to the motor and brake solenoid so that the brake is released and the motor drives the cab. It will be noted that two of the motor leads from contactor I5 are reversed so that the motor runs in one direction when the down contact [5 is energized and in the opposite direction when the up contact [4 is energized. The motor is thus made to run in such a direction as to reduce the error voltage to zero, and the cab is always driven toward the selected floor.

In operation, when a particular floor is selected, a tap 20, corresponding to the call button depressed, is connected to line 2| and an error voltage is produced across lines 2| and 25 which apply it to the error amplifier 24. The polarity of this voltage, which is dependent upon whether the cab is positioned above or below the selected floor, determines whether the up or down direction contactor is energized. The appropriate contactor is energized by the output of the error amplifier to close the motor and brake solenoid circuits, releasing the brake and causing the motor to run toward the selected floor, a direction which tends to reduce the error voltage to zero. As the elevator cab starts to move, the tachometer generates a direct current voltage which is opposed to the floor position signal and which causes the error voltage to be reduced and to reach zero before the cab reaches the selected floor level. Whenever the error voltage reaches zero, the contactor is deenergized, opening the motor circuit and applying the brake. The brake is thus applied at the proper distance from the floor to cause the cab to slide in one continuous motion into the proper fioor level and there come to rest. Should the cab stop short of the floor level for any reason, the error voltage will reenergize the proper contactor to drive the cab into proper alignment with the floor. If the cab overshoots the floor, the polarity of the error signal will be reversed so that the other contactor will be energized and the motor will cause the leveling correction to be made in the opposite direction.

Figure 2 is a schematic circuit diagram of a call and leveling system. Figure 2 can best be examined in conjunction with Figure 3 which shows the relationship of the relay coils and their associated contents. By placing Figures 2 and 3 in sideways alignment, the contacts of Figure 2 may be located by first locating the associated coil in Figure 3, dropping down the sheet to the point where the contact is marked, and then moving horizontally back to Figure 2 to the contact in question. A three phase alternating current motor 26, energized from main power supply lines II], I! and I2, is used to drive the elevator cab. Operation of the motor is controlled by up contactors C8 and down contactors CID. A conventional friction brake for stopping the cab is controlled by solenoid 21 which is energized simultaneously with the motor in a manner explained below. The brake arm and solenoid 21 are so arranged that the brake is released only when the solenoid is energized (whenever the motor current is closed), and will set if there is any interruption to the current supply.

The call and leveling systems may be considered as comprising three principal sub-circuits; namely, the call button circuit, indicated generally at 28, a rectifier output circuit, indicated generally at 29, and a control circuit, indicated generally at 30.

The rectifier circuit 29 is powered by the output of rectifier 3| and includes the brake solenoid 21 and up and down relay coils R8 and RI 0, which actuate up and down contacts 08 and Clfi. The brake solenoid 21 and the appropriate up or down relay coil are energized whenever power is supplied to the rectifier so that one function of the control circuit must be to govern the rectifier input.

The call button circuit 28 rovides a means of selecting the floor to which the elevator is to be driven and includes floor buttons Fl, F2, F3, F4, and F5 which are located on the respective floors of a building, and cab buttons Bl, B2, B3, B4, and B5 which are located within the cab. The depression of any of these buttons energizes a corresponding relay RI, R2, R3, R4, R5, closing a contact Cl, C2, C3, C4, or C5 to connect a particular tap of a floor level resistor network [8 to line 32. The depression of any of the call buttons also energizes relay coil R6 which controls the power supply to the control circuit.

The control circuit 30 governs the power input of the rectifier and determines whether the up or down relay is energized by the rectifier output. This circuit is energized from a secondary 33 of transformer 34, whenever relay R6 is energized and its contact C6 closed. Secondary 35 of transformer 36 provides the control voltage and is connected across the potentiometer coil l9 and the floor level resistance network l6 which are arranged in parallel. Tachometer 23, having an output resistance network indicated generally at 31, is connected in series with the potentiometer tap 22 which is moved relative to potentiometer coil IS in synchronism with the elevator cab position.

The floor signal tap 20 is connected to one of the input leads 33 of amplifier 24 and tachometer 23 and potentiometer tap 22 are connected to the other amplifier input lead 39. The output of error amplifier 24 operates polarized relay R1 which in turn energizes a succession of relays to close the rectifier input circuit. Polarized relay R1 also determines whether the up or down relay will be energized, along with the brake solenoid, by the output of rectifier 3|.

A more detailed description of the sub-circuit arrangements embodied in the control and leveling systems illustrated in the drawings follows.

Call button circuit The voltage for the call button circuit 26 is taken from power lines In and I2. Power line I0 is connected through fuse 40, lead 16 and line 4| to conductors 42 and 43. Line |2 passes through fuse 44 and line 45, which contains a reverse phase sequence relay 46, and the usual stop button 41, stop limit switch 48, governor switch 49, and release catch switch 50 to lead 5|.

The coil of the reverse phase sequence relay 46 is connected to power lines I0, I and I2 by leads 5'2, 53, and 54 respectively. The function of this relay is to prevent a contact, which normally keeps line 45 open, from closing if an improper phase sequence is present in the power supply lines Hi, H, and i2. The reverse phase sequence relay also prevents the contact from closing line 45 regardless of the phase sequence if any of the lines it, i, and |2 are removed, thereby preventing single phase operation of the motor. The operation of this relay is of no consequence to the present invention since, along with the stop button, limit switch, governor switch, and release catch switch, it constitutes a safety device which may be used with any call and leveling system.

Lead 5| contains the coil of relay R6 and is joined to conductor 55. A plurality of parallel lines, 56, 58, 6t, and 6|, join conductors 42 Each of the lines 56, 51, 58, 6!], and 6| contain a floor button Fl, F2, F3, F4, F5 and a relay coil El, R2, R3, R4, R5. Leads 62, 63, 64, 55, and. 56 join the conductor 43 with lines 56, 51, 53, 60, and 6| respectively. Each of the leads 52-66 contains a cab button BI, B2, B3, B4, B5. Thus, the circuit through relay R6 and any of the relay coils R4, R2, R3, R4, and R5 may be completed by depressing either of the corresponding cab or floor buttons.

Additionally, the relay circuit may be closed through a conductive path provided by lead 61, which contains four relay contacts C2 C22, C53, and C44 in parallel; and conductor 68. Five leads 12, 1|, 12, 13, and 14 connect conductor 68 and the lines 56, 51, 58, 60, and 6| respectively. Each 9 of the leads 10-14 contains a holding contact C3 I, C32, C33, C34, and C35 actuated by the relays RI, R2, R3, R4, and R5 respectively. The bolding contacts permit the relay circuit, energized by the call buttons, to remain energized until the elevator reaches the selected floor even though the particular button initially energizing the circuit is depressed only momentarily.

Control circuit Power for the control circuit is furnished by secondary 33v of transformer 34. Primary 15 of transformer 34 is connected across power lines I and II through leads 16 and 11 and fuse "I8. Conductors 8|! and 8| are joined to the ends of secondary 33; and primaries 82, 83, and 84 of transformers 85, 36, and 86 are connected in parallel across these conductors.

A transformer 86 has a secondary 81 which energizes the field B8 of tachometer 23 through rectifier 89, leads 90 and 9| and current limiting resistance 92. The tachometer output, which is proportional to the velocity of the cab, is carried by lines 93. and 94. Line 93 is connected to the tap 22 of potentiometer I9 and to one side of resistance 95. Line 94 is connected to the opposite end of resistance 95 through two parallel conductive paths. One path is constituted by line 96, itself having two parallel branches, one containin normally closed contact CI 6 of relay RI Ii and resistance 91, the other branch containing resistance 98. Line I08, which forms the second conductive path from line 94 to resistor 95-, contains a resistance net Work comprising Globar resistances IDI- and I02 in series with the parallel combination of Globar resistances I03 and HM. Resistor 99 joins line I95 and line I 00. The resistors I8I, I82, I83, I94 may be thyrite disks or any suitable nonlinear resistance material which has the property of varying its resistance in accordance with an inverse power of the applied voltage. With the elevator motor running near synchronous speed, this network provides a voltage signal which varies approximately as the fifth power of the tachometer voltage and consequently as the fifth power of cab velocity.

The output of tachometer 23' also energizes relay coil RI5 through leads 94 and IE5, and cur rent limiting resistor I89. Relay coil RI8 is energized through conductor I01, connected across lines 94 and I95. Conductor I91 contains a resistance I08 and resistance I99 shunted by a variable bypass tap II8. Relay I6 is adjusted to pull in or close the contact CIB, when the motor is traveling at substantially (about .8) synchronous speed. Relay R. is adjusted to close contact C55 shortly after the motor starts running (about 18 R. P. M).

The secondary 85 or" transformer 39 supplies voltage to the potentiometer I9 and the variable floor resistance network, shown generally at I8. Each endv or" secondry 85 is provided with a direct current rectifier III and H2. These ends are joined by contactor I I3. A tap I I4 is taken from the transformer secondary and is connected toone end of the resistor network I8, at H5, and to one end of the potentiometer coil I9. Lead- I I6 containing inductance II? and resistor II8 connects line II 9 to the opposite end of the potenti'omcter coil I9 to the opposite end of resistance network III, at I29. Resistance IIB is shunted by a variable by pass tap I2I. Lead I22 containin condenser I23 is connected across line H8 and the potentiometer coil I9.

The resistance network I8 comprises resistors- I24, I25, I26, I21, I28 and I39 connected in series across terminals H5 and I28. By-pass tap I3I is used to vary resistance I38. Taps I32 and I33, joined by resistance I39 pick off resistances I38 and I28 respectively. Taps I35 and I38 joined by resistance I81 are in contact with resistance I21. Taps I38, I49 and I II, connected through resistances M2, I43, I49 pick ofi resistances I26, I25 and I24 respectively. Conductor connected to resistance I25 and resistance I23. Five taps, I48, I41, I48, I49 and I59 are provided to connect line 32 with a resistor network I8. Each of these taps is connected to line 32 through a contact CI, C2, C3, cs, or C5, operated by relay RI, R2, R8, R4 or R5 respectively. The voltage drop between line 82 and line H8 thus depends upon which of the relay contacts CI, 02, C3, C4 and 05 connects the resistor network to line 32.

Amplifier 24 is provided with two input leads 38 and 99. Input 88 is grounded through line 32 while input 89 is connected to tap I5I of resistance I52. One end of resistance I52 is connected to line 32 and the opposite end is connected to a tap I53 of resistance 85. The amplifier comprises two twin triode tubes I54 and IE5 having the usual cathode heating elements, the elements and circuits being omitted for simplicity. Tube I54 has a grid I58 connected through resistance I51 to input lead 39. A second grid I58 is connected to the other amplifier input lead 38. Two cathodes I59 and IE9 are inter-connected and then grounded through resistance I8I. Two plates are provided, IE2 and I93, which are connected through conductors I64 and I to grids I88 and I81 of tube I55.

Tube I55 has two cathodes I68 and I19 which are tied together by lead I1I connected across relay coil R1. The coil of R1 is grounded through lead I12 and resistance I13. Tube I55 has two plates I14 and I15. Plate voltage is furnished by the secondary winding I18 of transformer 85. Each end of secondary I16 is provided with a direct current rectifier I11 and I18 and the ends are tied together through lead I89. A center tap I8I is connected to line 32 and also to line I88 through condenser I82. Line I89 containing inductance I83, is joined to plates I14 and I15 and is provided with a tap I84 in contact with resistance I85. Resistance I85 is connected in series with resistances I86 and I81 across lines I64 and I95.

Relay coil R1 is a polarized relay and its contact 01 has three distinct positions, an open po sition, one in which it closes line I88, and one which. closes line I99. Lines I88 and I99 are joined to conductor I9I, containing contact I92 of thermal time delay element I93 which is connected in series with resistance I89 across lines I94 and I95. Conductor I9I is connected to one side of secondary 33 of transformer 34 through lead I94. Line I88, which contains relay coil RII and contact C4I of relay RI I, is connected to the opposite side of secondary 33 through line I95. Likewise, line I99, which contains relay coil RI2 and its contact C42, is joined to line I95. Relay coil R2I is shunted across relay coil RI! and contact C4I, through lead I98. Relay R22 is similarly shunted across relay RI2 and its contact C42, by lead I91. Conductor I98interconnects lines I88 and I90.

Normally closed contacts, CI3 and. C14, operated by relay coils RI3 and RI4 are connected in series between conductor I98 and line I95. Relay coil RI5 is a polarized relay, similar to relay R1, and has a three position contact, CI5, which 11 is adapted to close the circuit between lines H34 and I25 through either lead 200 or lead 20I and relay coil RI4 or RI3, respectively.

The control circuit also includes a branch comprising lead 202 which connects one input terminal of rectifier 3| to power line 52 through contact CI! of relay coil RH and lead 45. The other input terminal or rectifier 3| is connected to power line I through lead 203 and line It. Conductor 204, containing relay coil RI'I and resistors 205 and 200, is connected across lines 45 and 01. Conductor 204 also has two parallel branch lines placed between the resistances 2E5 and 206. One branch line 201 contains relay coil RIB, contact CI2 of relay RI2 and normally closed contact C20 of relay R20. Branch line 208 contains relay coil R20, contact CII of relay RH, and normally closed contact CI8 of relay coil RI8. Thermal relay element 2I0, having normally closed contact 2| I, placed in line 4!, is connected across lines 4| and 202 through conductor 2I2 and normally closed contact C24 of relay R24.

Rectifier circuit The rectifier circuit is a direct current circuit supplied by the output of rectifier 3|. Two lines 2M and 2I5 are connected to terminals H6 and 2!! of rectifier 3|. The brake solenoid 21 is connected across lines 2 I4 and 2I5 through line 2|8 containing contact C23, actuated by relay R23. Line 2I8 has two parallel branches, one containing contact C33, the other containing contact C40, which contacts are actuated by relays RB and RIO respectively.

The motor direction control relays, up and down relays R8, R|0 are connected to line 2|5 through lines 220 and MI and contacts C48 and C50 which are actuated by relay coils Bill and R20. Lines 220 and HI are joined to line 2I4 through line 222 containing relay coil R23, car door switch 223 and hatch door interlock 224. Relay coil R23, when energized, closes contacts C43 in power lines II and I2 while the up and down relays R8 and RI 0 control the up and down contactors C8 and C|0 in the motor power circuit. Relays R24 and R25 are also connected across lines 2I4 and 2|5 in parallel. These relays actuate contacts C24 and C25 respectively.

Operation of the system To illustrate the operation of the circuit, suppose that the cab is stopped at floor 5, and that a passenger in the cab desires to be taken to floor 3 Or that someone is waiting for the cab on floor 3. Eithe the passenger presses button B3 in the cab or the person waiting presses floor button F3. In either case, relays R3 and R5 are energized by the current flowing through lines 4| and 5|.

Relay RE which, when deenergized, shorts the input of the amplifier to ground through normally closed contact C36 and line 32, upon energization, opens contact C35 and closes contact CE. Contact CE in line 00 closes the circuit from secondary 33 of transformer 34 to the primaries 83 and 84 of transformers 30 and 8'0.

Relay R3 closes contacts C3 and C33. C33 is a holding contact while C3 connects tap I43 of floor level resistor network I8 to line 32. This tap establishes the floor level signal in that the voltage from it to ground is proportional to the distance of the selected floor from an arbitrary reference point. Tap 22, due to the mechanical linkage of either the tap or the coil II! with the motor 26, moves relative to the coil and at all times is in contact with the coil at a point such that the voltage across the coil is proportional to the height of the cab from the same arbitrary reference point. The voltage across line 32 and tap 22 thus represents an error voltage indicating by its magnitude and polarity the relative position of the cab and the floor selected. This error voltage is applied, through lines 32 and 93, across resistance I52.

With the cab at rest, the tachometer output is zero and the error voltage comprises only the floor signal voltage minus the cab signal voltage. With the transformer polarities arranged as shown, tap 22 will be at a higher potential than tap I40, therefore amplifier input lead 39 will be positive with respect to amplifier lead 38.

The potential of grid I56, which is connected to lead 39, is raised causing a greater plate current to flow from plate I33 to cathode I52. Plate I53 becomes less positive, lowering the potential on grid I61 of tube I55. As grid I61 becomes more negative, the current flowing in the plate cathode circuit including plate I15, cathode I68 and that portion of the coil of relay R1 shown to the left of grounded tap I12, decreases.

Simultaneously there is negative feed back to the left hand grid I56 of tube I54 in that the cathode I59 in becomin more positive increases the voltage drop across resistance I6 I. This raises the potential of cathode I60 relative to grid I58 which is grounded directly through input lead 38. Lowering the cathode to grid potential of grid I58 decreases the plate current flowing from plate I62 to cathode I60 thereby raising potential of the former and also of the right hand grid I56 of tube I55. The higher voltage on grid I66 causes a larger plate current to flow through that portion of relay coil R'I shown to the right of grounded tap I12. In consequence of the increased current flow in the right hand branch of the relay coil R1 and the decreased flow in the left hand branch, the contact CT is magnetically forced to the left, closing line I88.

When line I is closed by contact C1, relay RI I is energized through lead I98, and closed contacts CI3, CI4. Relay RZI is simultaneously energized through lead I88 and I96. Relay 2| closes contact C2| in line 61 and hence, a circuit across line 4|-55 is completed through leads 61, 68, I2 and 58 causing the relays R3 and R6 to hold in (remain energized) during the rest of the cycle of operation even though the call button is released.

Relay RI I actuates contact CI I, closing the circuit across lines 45 and 61 to energize relay coils RH and R20. Relay RII closes contact CII completin the circuit to the rectifier 3| through lines 45 and 203. Relay R20 simultaneously opens contact C20 to prevent any current from flowing through line 201 and closes contact C50 energizing down relay RI 0 and relay R23. Relay R23 actuates contacts C23 in line 2 I8 and C43 in power lines II and I2, while relay RIII actuates contacts CIO and C40 closing the brake solenoid circuit across lines 2|4 and 2|5 and closing the motor circuit to power lines I0, I I and I2 to cause motor operation in the down direction.

Thus, the brake is released and a voltage is supplied to the motor causing it to drive the cab downwardly toward the selected floor. As the elevator accelerates the tachometer voltage will increase and relay RI5 is sufliciently energized thereby to close contact CI5, energizing relay RI3. Relay R|3 opens contact C|3 in series with relay- RI I, simultaneously closing a holding 0011-.- tact C53 in the call button circuit. Relay RH however will remain energized through holding contact C4! which is connected in parallel with the contacts C l 3 and CH.

The tachometer voltage also energizes relay Rlfiwhich is adjusted to open contact Clfi when the motor approaches synchronous speed, removing resistor 91 from line 96. Resistance 98 is then of the combined potentiometer, fioor resistance network, and velocity voltages becomes zero. When the amplifier input voltage is thereby reduced to zero, relay R1 is deenergized and contact C1 moves to a neutral position, deenergizing relays RI l and R2 I. This opens contacts C H and 02! which interrupts the rectifier supply circuit by deenergizing relay RI! and opening contact CIT. Upon deenergization of the rectifier 3| the current to brake solenoid 2! is interrupted and the brake is applied while the down contacts C16 in the motor circuit are opened to deenergize the motor. The cab then slides into the floor levelwhere it is brought to rest by the action of the friction brake.

It will be noted that once deenergized, it is impossible for either of the relays RI l or R12 to bereenergized until the cab velocity reaches approximately zero since the contact (H3 in series with these relays is opened. Relay R2! can, however, be reenergized thus keeping the call button circuit closed.

Thermal time delay element I93, connected across the lines H54 and I95, is energized whenever power is supplied to transformer 3-55. The time delay element has a contact I92 which prevents current from flowing through relay coils RI and R12 until the control circuit has been energized for a sufficient length of time to permit the tubes !54 and I55 to be properly heated. After a predetermined interval of time, thermal element I93 becomes heated, closing contact 592 to permit functioning of relays HI I and RI 2.

Other precautionary devices include relay coil R24 having normally closed contact C24, and thermal relay 210 having a normally closed contact 2| I. Thermal element 21!} is connected in series with contact 024 across input lines 4! and If power should be supplied to the rectifier for an appreciable time and contact C24 remains closed, the element 2i 9 will open contact 2 I I to interrupt power supply to the call buttons. However, relay R24 is connected, across the brake solenoid 27 so that if the solenoid and up or down relay coil is energized contact 024 will open removing element 2!!) from the cirult so that contact 211 will remain closed. A second relay coil R25 is energized whenever power is available in the rectifier output circuit across lines 2M and 2| 5. This relay coil has a normally closed contact C25 which opens the fioor button circuit to prevent a call, made while the cab is in motion, while affecting cab movement until after the cab has been stopped at the already selected floor.

Having described our invention, we claim:

1. An elevator system comprising a cab, a mo.- tor for driving said cab, motor direction control relays, a control circuit, and means for operating said relays in response to said control circuit, said control circuit having an applied electromotive force equal to the sum of three voltages, the first voltage being dependent upon the position of the cab relative to a predetermined reference, the second voltage being dependent upon the position of a selected floor relative to the same reference and the third voltage being dependent upon the, velocity of the cab.

2. An elevator system comprising a cab, a motor for driving said cab, a brake for stopping said cab, means for applying said brake whenever the motor is deenergized', and means for controlling the periods ofv motor energization in response to a control. circuit, which circuit is characterized by an 'electromot-ive force consisting of the sum of a voltage dependent upon the position of said, cab relative to a predeterminedv reference, a voltage dependent upon the position of the selected fioor relative to the same arbitrary reference and a voltage dependent upon the velocity ofv the cab.

3. In an elevator levelling system including acab and a motor, the combination of a brakefor stopping said cab, a control circuit, means for applying said brake in response to said control circuit, said control circuit having an applied electro-motive force consisting of a first voltage dependent upon the position of the cab. relative to an arbitrary reference, a second voltage dependent upon the position of a selected floor relative to the same reference, and a third voltage dependent upon the velocity of the cab, said first voltage and said third voltage having a polarity opposed to that of said second volt age whereby the brake, is applied at varying cab positions relative to the selected fioor, which positions depend upon the velocity of said cab.

4:. In an elevator system having a plurality of call buttons. associated with various floors of a building, the combination of a cab, a motor for driving said cab, a brake, means for applying said brake whenever said motor is deenergized,

motor direction control contacts, and means including a polarized'relay for operating said contacts in response to a control circuit, said control circuit including a tachometer in mechanical' interconnection with said motor whereby the tachometer output voltage is proportional to the cab speed, a control voltage supply, a floor resistor network connected to said control volt age supply and having a plurality of taps adapted for connecting said resistor network to said control circuit, the particular tap interconnecting said fioor resistance network and said control circuit being determined by the depression of a call button, the voltage across one end of the resistance network and said tap b6 ing dependent upon the height of the door, as sociated with said depressed call button, from a predetermined reference, a potentiometer connected to said control voltage supply and having a coil and a tap, said potentiometer coil and said tap being moved relative to each other in synchronism with the movement of said cab so that the voltage across one end of the potentiometer coil and tap is proportional to the height of said cab from said predetermined reference point, the sum of said tachometer voltage, potentiometer voltage and resistance network voltage controlling said polarized relay whereby 15 the motor direction control contacts are operated in accordance with the polarity of the control circuit voltage and when said voltage reaches zero, the motor will be deenergized and the brake applied.

5. In an elevator system for levelling a cab with various floors of a building, a motor for driving said cab, motor direction control contactors, a circuit for controlling said motor di rection control contactors, and means in said circuit for determining the position of said cab relative to a selected floor, said means comprising a control voltage supply, a resistor network connected to said control voltage supply and having a plurality of taps adapted for connecting said resistor network to said control circuit, the voltage drop across said resistance network to the particular tap interconnecting said floor resistance network and said control circuit being dependent upon the height of the selected floor from a predetermined reference, and a potentiometer connected to said control voltage supply and having a coil and a tap, said potentiometer coil and said tap being moved relative to each other in synchronism with the movement of said cab so that the voltage across the potentiometer coil and tap is proportional to the height of said cab from said predetermined reference point.

6. In an elevator levelling system having a cab, a motor for driving said cab, motor direction contactors and a circuit for controlling said direction contactors, means in said circuit for determining the position of said cab relative to a selected floor, said means comprising a control voltage supply, a variable floor resistor connected to said control voltage supply, means for varying the voltage across said resistor whereby a specific voltage is impressed upon the control circuit for each of the various floors of a building, and a potentiometer connected to said control voltage supply and having a coil and a tap, said potentiometer coil and said tap being moved relative to each other in synchronism with the movement of said cab so that the voltage across the potentiometer coil and tap is proportional to the height of said cab from said predetermined reference point and is opposed to said floor resistor voltage.

7. In an elevator system having a cab, a motor for driving said cab, and a brake adapted to set whenever the motor is deenergized, means for deenergizing said motor and applying said brake at a distance from a selected floor dependent upon the velocity of said cab, said means including a tachometer in mechanical interconnection with said elevator motor whereby the tachometer output voltage is proportional to the cab speed, and a non-linear resistance network for varying said tachometer output voltage as a predetermined function of cab speed.

8. Apparatus for automatically levelling a cab in an elevator system having a motor, the energization of said motor being electrically controlled, said apparatus comprising a control circuit, means for applying to the control circuit an electrical quantity proportional to the height of said cab above a reference, means for applying to said circuit a standard electrical quantity representing the height at which the cab is to be stopped, said quantities being compared in said control circuit so that an electrical quantity results from said comparison when the circuit is unbalanced, control means to which said resultant electrical quantity is applied to govern 16 the motor energization whereby the unbalanced state of said control circuit is decreased.

9. Apparatus for automatically levelling a cab in an elevator system having a motor, the energization of said motor being electrically controlled, said apparatus comprising, a control circuit, means for applying to the control circuit an electrical quantity proportional to the height of said cab above a reference, means for applying to said circuit a standard electrical quantity representing the height at which the cab is to be stopped, and means for applying to said circuit an electrical quantity proportional to the velocity of said cab, said quantities being compared in said control circuit so that an electrical quantity results from said comparison when the circuit is unbalanced, control means to which said resultant electrical quantity is applied to govern the motor energization whereby the unbalanced state of said circuit is decreased.

10. An elevator levelling system comprising a cab, a motor, a brake for stopping said cab, a control circuit, means for applying said brake in response to said control circuit, said control circuit having an applied electromotive force consisting of a first voltage dependent upon the position of the cab relative to an arbitrary reference, a second voltage dependent upon the position of a selected floor, and a third voltage dependent upon the velocity of the ca b, said third voltage being generated by a tachometer mechanically interconnected to said motor, said third voltage passing through a resistance network comprising non-linear resistance elements whereby said third voltage varies as a function of cab velocity, said third voltage having a polarity similar to said first voltage and opposed to that of said second voltage whereby the electromotive force of said control circuit will become zero at a cab position relative to a selected floor, determined by the velocity of said cab, said means for applying said brake being operative whenever the electromotive force of said control circuit becomes zero.

11. In an elevator levelling system including a cab and a motor for driving the cab, the combination of a brake for stopping said cab, a control circuit, means responsive to said control circuit for applying said brake, said control circuit having an applied electromotive force consisting of a first voltage dependent upon the position of the cab relative to an arbitrary reference, a second voltage dependent upon the position of a selected floor relative to the same reference, and a third voltage dependent upon the velocity of the cab, means including a non-linear resistance network and a relay responsive to said third voltage for varying said third voltage as an exponential power of cab velocity when said motor is running near synchronized speed or linearly with cab velocity when the motor is running at a lesser speed.

12. An elevator levelling system comprising a cab, a motor for driving said cab, motor direction contactors for controlling the energization of said motor, a control circuit for governing said contactors, a plurality of call buttons associated with various floors of a building, a control voltage supply, a variable floor resistor connected to said control voltage supply and having a plurality of taps adapted to interconnect said resistance and said control circuit, depression of one of said call buttons determining the particular tap interconnecting said resistor and said control circuit, whereby the voltage drop across said resistor is made proportional to the height of the floor associated with said depressed call button above a predetermined reference, a potentiometer connected to said control voltage supply and having a coil and a tap, said potentiometer coil and said tap being moved relative to each other in synchronis-m with the movement of said cab, so that the voltage drop across the tap and one end of the potentiometer coil is proportional to the height of said cab from said predetermined reference point, said voltage drops being compared in said circuit so that an error voltage results when said cab and said floor are not aligned, and means including a polarized relay to which said error voltage is applied to govern said contactors.

13. An elevator levelling system comprising a cab, a motor for driving said cab, motor direction contactors for controlling the energization of said motor, a control circuit for governing said contactors, a plurality of call buttons associated with various floors of a building, a control voltage supply, a variable floor resistor connected to said control voltage supply and having a plurality of taps adapted to interconnect said resistance and said control circuit, depression of one of said call buttons determining the particular tap interconnecting said resistor and said control circuit whereby the voltage drop across said resistor is made proportional to the height of the floor associated with said depressed call button above a predetermined reference, a potentiometer connected to said control voltage supply and having a coil and a tap, said potentiometer coil and said tap being moved relative to each other in synchronism with the movement of said cab, so that the voltage drop across the top and one end of the potentiometer coil is proportional to the height of said ca'b from said predetermined reference point, a tachometer in mechanical interconnection with said motor and in electrical interconnection with said control circuit whereby a voltage proportional to the speed of said cab is introduced into said circuit, said voltages being compared in said circuit so that an error voltage results when said cab and said floor are not aligned, and means including a polarized relay to which said error voltage is applied to govern said contactors.

14. In an elevator system having a cab, a motor for driving said cab, means for deenergizing said motor when said cab is at a distance from a selected fioor, said distance varying in accordance with the velocity of said cab, said means including a tachometer in mechanical interconnection with said elevator motor, said tachometer being continuously effective to generate an output voltage proportional to the cab speed.

15. In an elevator system having a cab, a motor for driving said cab and a brake adapted to set whenever the motor is deenergized, means for applying said brake at a distance from a selected floor dependent upon the velocity of said cab, said means including a tachometer in mechanical interconnection with said elevator motor whereby the tachometer continuously generates an output voltage proportional to the cab speed.

16. In an elevator system, means for determining the relative position of a cab and a selected floor, said means comprising a control circuit, said control circuit having a first voltage applied thereto, said first voltage being characteristic of the floor at which the cab is to be stopped, and a second voltage applied thereto, said second voltage being variable in accordance with the position of the cab.

17. In an elevator system including a cab and a motor for energizing said cab, means for automatically levelling the cab with a selected floor, said means including a control circuit for governing the periods of motor energization, said control circuit having a signal continuously produced therein dependent upon the position of the cab relative to the selected floor.

18. In an elevator system including a cab, a motor for energizing said cab, and a brake for stopping said cab, means for bringing the cab to rest at a selected fioor, said means including a control circuit for governing the period of application of the brake, said control circuit having a voltage signal continuously produced therein dependent upon the position of the cab relative to the selected floor.

19. In an elevator system including a cab, a motor for driving said cab, and a brake for stopping said cab, means for automatically levelling said cab with a selected floor, said means including contactors for deenergizing said motor and applying said brake, and a control circuit for actuating said contactors while said cab is displaced a predetermined distance from said floor.

20. In an elevator system including a cab, a motor for driving said cab, and a brake for stopping said cab, first means for automatically leveling said cab with a selected floor, said first means including a control circuit and second means responsive to said control circuit for deenergizing said motor and applying said brake, said control circuit having a signal produced therein dependent upon the position of the cab relative to the selected floor, and a second signal produced thereindependent upon the velocity of said cab, said control circuit also including third means for comparing said signals.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,709,102 Waite et a1 Apr. 16, 1929 1,781,443 Rodman Nov. 18, 1930 2,145,809 Taylor 1 Jan. 31, 1939 2,403,125 Santini July 12, 1946 

